XX INTRODUCTION. 



mercury freezes, the human beings subjected to it can take 

 their wonted exercise and perform their accustomed duties. 

 Nay, there are cases to shew that certain animals may have 

 the great mass of their fluids frozen, and yet be preserved 

 from death. Fishes have been dragged up from the circum- 

 polar seas, which froze, as the nets were in the course of be- 

 ing raised, into masses so hard that they might have been 

 shivered to pieces by a stroke, and yet they would recover if 

 thawed. A common eel has been frozen like a piece of ice, 

 and been conveyed in a state of torpor thousands of miles, 

 and then been restored to its state of activity by the applica- 

 tion of warmth. 



But there are degrees of cold to which the frame of cer- 

 tain animals in their state of activity is unsuited. Nature 

 here provides a remedy by rendering them torpid in the ab- 

 sence of necessary heat. Thus innumerable insects are ren- 

 dered insensible to the action of the external air during the 

 winter season. In the case of the animals termed hyber- 

 nating, sensation becomes suspended, the fluids of the body 

 circulate more slowly, and respiration and all the vital ac- 

 tions become less active. The torpor of the creature is like 

 death rather than sleep, and yet enough of vital action re- 

 mains to preserve it from the external agents, which, in its 

 condition of activity, would destroy it. It remains as if dead, 

 but as soon as the air recovers the due warmth, the vital 

 functions of the animal regain their powers, and it awakens 

 from its long trance. The dormouse, the marmot, the hedge- 

 hog, the bat, are with us familiar examples of animals that 

 undergo this state of winter sleep, during which they are 

 so dead to feeling that they may be tossed about, nay, 

 sometimes have the limbs separated from the body, or the 

 most vital parts exposed, without their exhibiting symptoms 

 of sensation. The swallow, which migrates to us in the 

 early part of summer, quits us on the approach of the colder 

 season. But some, too young or too feeble for flight, remain 

 behind. These betake themselves to holes in walls and the 



